The final active block in an RF transmitter chain is typically a power amplifier (PA), which functions to deliver a high-power output to an antenna. The antennas are typically designed to be 50Ω. This nominal value, however, can be greatly affected by environmental and frequency variations. Therefore, an adaptive matching network containing tunable components is typically placed between the power amplifier and the antenna in order to transform the antenna's impedance to that desired by the power amplifier for maximum power delivery.